1. Field of the Art
This invention relates to a flexible tube which is particularly useful, for example, as a biopsy channel or guide tube to be incorporated into an endoscopic insertion instrument or as a catheter or the like, and a method for manufacturing such guide tubes.
2. Prior Art
Generally, endoscopes which are in use in medical fields are constituted by a manipulating head assembly to be gripped by an operator and an insertion instrument which is extended forward from the manipulating head assembly for insertion into a patient""s body cavity. By way of properties, an endoscopic insertion instrument can be divided into three sections, i.e., a rigid tip end section which is provided at a fore distal end of the insertion instrument, an angle section which is connected to a proximal end of the rigid tip end section, and an elongated flexible body section which is connected between a proximal end of the angle section and the manipulating head assembly. Endoscopic observation means are provided on the rigid distal end section for observation of intracavitary portions, including an illumination window or windows having a light emitting end of a light guide fitted therein for projecting illumination light, and an observation window having an optical lens system fitted therein for picking up optical images of intracavitary portions. Further, an exit hole of a biopsy channel is opened in the rigid tip end section for projecting forceps or other biopsy or surgical instrument into a body cavity therethrough.
The angle section is a part which can be flexibly bent into an angular form by remote control from the manipulating head assembly. The flexible body section has a flexible structure which is bendable in arbitrary directions along a path of insertion into a body cavity. Various component parts which are fitted in or threaded through the flexible body section should also be flexible in bending directions of the insertion instrument. In this connection, the biopsy channel is extended coextensively through the insertion instrument, more specifically, from a fore distal end of the insertion instrument up to an entrance hole or an entrance way which is provided on the manipulating head assembly. Forceps or other instruments which are introduced into the biopsy channel through the entrance hole are projected into a body cavity through the exit hole which is formed in the rigid tip end section of the insertion instrument to make a necessary treatment. Therefore, the biopsy channel is required to be flexible in bending directions and is usually constituted by a flexible tube. The biopsy channel which is fundamentally provided for insertion of biopsy instruments is also used as a suction passage at the time of sucking out body fluids or the like. In addition to a biopsy channel, a flexible tube of similar nature is also fitted in the endoscopic insertion instrument to serve as an air/water feed tube for the purpose of washing the observation window.
In addition to the afore-mentioned flexibility, the flexible tubes which are used in medical treatments as endoscopic biopsy channels or for other purposes are required to have satisfactory properties in shape retainability including anti-crushing strength, anti-kinking strength, anti-rupturing strength, air tightness, water tightness, resistance to chemicals, feasibility of disinfection by washing, biotic suitability or safety etc. Especially, a flexible tube to be use as an endoscopic biopsy channel should be formed of a material which is slippery and of low frictional coefficient in order to ensure smooth insertion of various instruments. The inside diameter of an endoscopic biopsy channel is determined depending upon outside diameters of endoscopically inserting instruments, and is normally in the range of 1 mm to 5 mm. Besides, in order to make the outside diameter as small as possible, a flexible tube for a biopsy channel is usually arranged to have a minimum necessary wall thickness.
For instance, disclosed in Japanese Patent Publication H7-45219 is a flexible tube which was developed to meet the above-mentioned requirements in properties. This known flexible tube is of a laminated structure consisting of an inner layer and an outer layer. The inner layer is formed by extruding a crystalline polymer resin consisting of a fluorine resin or the like into a tubular form. This inner layer is particularly so arranged as to have properties which are required of the inner layer of the biopsy channel, namely, to have suitable properties in slipperiness, low friction coefficient, resistance to chemicals, feasibility of disinfection by washing and biotic safety, in addition to air- and water-tightness. However, the crystalline polymer resin itself is inferior flexibility. Therefore, the thickness of the inner layer is reduced as much as possible for the purpose of imparting flexibility thereto, at the sacrifice of strength. For these reasons, the outer layer needs to be imparted with necessary properties in strength, including shape retainability and anti-rupturing strength, in addition to flexibility. Therefore, the outer layer is formed of a thermoplastic resin, desirably urethane resin. In order to enhance the strength of the outer layer, a reinforcing layer is embedded in urethane resin or a reinforcing layer is sandwiched between urethane resin layers. Mesh-like knit fabric of metal fiber is used as a reinforcing layer for the purpose of ensuring flexibility in bending directions.
The arrangement of above-described prior art flexible tube can be advantageously used as an endoscopic biopsy channel. However, this prior art flexible tube still has a number of problems. One problem relates to the wall thickness of the flexible tube. The use of the outer layer, having a reinforcing layer sandwiched between urethane resin layers, makes reductions in wall thickness very difficult. In addition, reductions in wall thickness are also difficult with regard to the inner layer which is formed by extrusion molding. Thus, the prior art flexible tube has limits in reducing the wall thickness of the flexible tube as a whole.
In the case of an endoscope which is designed for medical use, it is desirable for the insertion instrument to be as thin as possible from the standpoint of reducing pains on the part of patients and facilitating passage through a narrow duct. Recently, the insertion instrument itself of an endoscope as well as internally fitted members of the insertion instrument are reduced in diameter almost to ultimate limits. Nevertheless, regarding the biopsy channel which occupies a relatively large space within the endoscopic insertion instrument, use of a flexible tube which is thinned down in wall thickness and in diameter and yet can meet the above-mentioned requirements in properties can contribute significantly in further reducing diameters of endoscopic insertion instruments.
On the other hand, as for a flexible tube which is intended for use as an endoscopic biopsy channel or for other medical use, Laid-Open Japanese Utility Model H4-47402 discloses a flexible tube construction having an inner layer or inner tube of fluororesin wrapped in a helical metal wire winding, and an outer layer of urethane resin which is laminated around the inner layer. In the case of this prior art flexible tube having a reinforcing layer formed directly around the outer periphery of the inner layer, the outer layer can be constituted by a single urethane resin layer. Therefore, since the properties such as anti-kinking strength, shape retainability and anti-rupturing strength can be covered by the outer layer, it becomes possible to reduce the wall thickness almost to an ultimate limit. However, the use of a helical metal wire winding as a reinforcing layer is insufficient in guaranteeing required shape retainability and strength of the biopsy channel particularly when a load is exerted in a twisting direction.
Further, the above-mentioned properties such as air tightness, water tightness, slipperiness, low friction coefficient, resistance to chemicals, feasibility of disinfection by washing and biotic safety are properties which are required of interior and exterior surfaces of a flexible tube, and do not necessarily have direct relation with the wall thickness. Therefore, it is desirable for the inner layer to be formed as thin as possible. However, the inner layer of the flexible tube in the above-mentioned Laid-Open Japanese Utility Model H4-47402 is formed by extrusion molding.
Further, disclosed in Laid-Open Japanese Patent Specification H5-95892 is a flexible tube having a tubular inner layer which is formed of a tape with necessary properties. From the standpoint of reducing the wall thickness, it is easier to form a tubular body by the use of a tape than forming a tubular layer by extrusion molding. The tube which is disclosed in Laid-Open Japanese Patent Specification H5-95892 employs a tape of a non-calcined tetrafluoroethylene resin in forming a tubular body. More specifically, an inner layer is formed by helically winding a tape material around a core wire in such a way that adjacent helices are overlapped one on the other to a predetermined extent, and then a reinforcing layer is formed by winding a stainless steel filament around the outer periphery of the inner layer, followed by sintering in a heating furnace to connect tightly to each other the overlapped portions of adjacent helices as well as the tape and the steel wire filament. Further, around the inner and reinforcing layers thus formed, an outer layer is formed by winding a non-calcined tetrafluoroethylene resin tape, and the resulting tube assembly is fired again in a heating furnace to connect the inner and outer layers integrally to each other.
In this connection, in forming a tubular inner layer by the use of a tape, it is important to over the adjacent helices to a predetermined extent in order to ensure air- and water-tightness which is essentially required of the inner layer. This however results in variations in thickness of the inner layer, which contains alternately a thick portion and a thin portion. Therefore, an instrument which has been inserted into a biopsy channel has to ride over the thick portions as it progresses toward an exit of the biopsy channel. For this reason, the flexible tube which is disclosed in Laid-Open Japanese Patent Specification H5-95892 is not necessarily suitable for use as a biopsy channel to be incorporated into an endoscopic insertion instrument, considering its non-smooth interior surface conditions.
Further, for the purpose of turning into a desired direction a rigid tip end section which is provided with illumination and observation windows along with an exit opening of a biopsy channel, an angle section is provided on the proximal side of the rigid tip end section. This angle section is flexibly bent into angular forms by remote control from the side of a manipulating head assembly of an endoscope. In this regard, in order to permit an operator to change the direction of observation view field, normally the angle section is arranged to be angularly flexible through 180 degrees or more. In some cases, there arises a necessity for inserting an instrument into a biopsy channel even when the angle section is in an angularly bent form. On such an occasion, the inserted instrument is forcibly pressed against inner surfaces of the angle section, on the outer side of the bend, as it progresses toward an exit at the distal end of the rigid tip end section.
As discussed above, in a case where the wall thickness of an inner layer of a flexible tube is reduced almost to an ultimate limit, it is very likely that repeated insertions of biopsy or surgical instruments can cause frictional wear or damages to certain localities of the inner layer and result in inward exposure of the outer layer through ruptured portions of the inner layer. This of course detrimentally affects the feasibility of disinfection by washing and resistance to chemicals on the interior side of the flexible tube. Therefore, in developing a flexible tube with interior surfaces of suitable properties for use as a biopsy channel on a medical endoscope, there have been limits to the reduction of wall thickness of an inner layer of the flexible tube, making it extremely difficult to reduce the diameter of the endoscopic biopsy channel.
In view of the foregoing situations, it is an object of the present invention to provide a flexible tube with an extremely thin inner layer which is almost free from frictional wear or damages by frictional contact, and a method for manufacturing such a flexible tube.
It is another object of the present invention to provide a flexible tube which can be reduced in diameter, without sacrificing properties which are required for application to medical diagnostic or therapeutic instruments.
It is still another object of the present invention to provide a flexible tube of the sort as mentioned above, which can contribute to reduce the outside diameter of an endoscopic insertion instrument when applied as a biopsy channel of the insertion instrument.
In accordance with the present invention, in order to achieve the above-stated objectives, there is provided a flexible tube, which comprises: an outer layer including a main tube body layer formed of a thermoplastic synthetic resin in a predetermined thickness, and a reinforcing layer provided integrally on the inner side of the main tube body layer; and an inner layer formed of a thin film of air tight and low friction material provided on the inner side of the reinforcing layer; the inner layer being formed by rolling a thin film into a tubular form in such a way that opposite sides of the thin film are overlapped one on the other to a predetermined degree to form a thick wall portion of a predetermined width extending longitudinally of and at one angular position of the tubular inner layer.
The inner layer which is formed into a tubular shape contains a thick wall portion. However, except the thick wall portion extending in the axial or longitudinal direction, the inner layer contains no other thick wall portions which extend in other directions on the inner periphery of the inner layer. The inner layer is formed of a thin film substantially of uniform thickness, which is rolled on itself at least by one turn and such that one lateral side of the thin film is overlapped on the other lateral side to a predetermined degree to formed a thick wall portion of a predetermined width extending in the longitudinal direction of the inner layer.
The flexible tube according to the present invention can be advantageously used as a biopsy channel of an endoscopic insertion instrument.
Namely, according to the present invention, there is provided a flexible tube to be fitted in an insertion instrument of an endoscope to serve as a biopsy channel for insertion of biopsy or surgical therapeutic instruments, the flexible tube comprising: a laminated multi-layer structure including an outer layer including a main tube body layer formed of a thermoplastic synthetic resin in a predetermined thickness, and a reinforcing layer provided integrally on the inner side of the main tube body layer, and an inner layer formed of a thin film of air tight and low friction material provided on the inner side of the reinforcing layer; the inner layer being formed by rolling a thin film into a tubular form in such a way that opposite sides of the thin film are overlapped one on the other over a predetermined width to form a thick wall portion of a predetermined width extending in the longitudinal direction of the inner layer; and the thick wall portion being located in an angular position of the biopsy channel where the biopsy or surgical instrument are slid against an inner surface of the biopsy channel when an angle section of the endoscopic instrument is flexibly bent into an angular form.
In a case where the angle section of the endoscopic insertion instrument is flexibly bendable at least in two predetermined directions, preferably the inner layer is formed of a plural number of thin films to provide longitudinal thick wall portions of a predetermined width at such angular positions of the inner layer that each is located on the outer side of a bend when the angle section of the endoscopic insertion instrument is bent in either one of the two directions.
The inner layer is formed of a thin film sheet which possesses necessary properties for the inner surface of the flexible tube. In the case of an inner surface of a biopsy channel of an endoscopic insertion instrument, it is required to have satisfactory properties in air tightness, liquid tightness, slipperiness, resistance to chemicals, feasibility of disinfection by washing, biotic safety etc. In order to meet these requirements, the thin film sheet for the inner layer is preferred to be of either non-calcined tetrafluoroethylene resin or non-calcined hexafluoroethylene resin. On the other hand, the outer layer of the flexible tube is composed of the above-mentioned main tube body layer and reinforcing mesh layer and required to have sufficient strength in shape retainability and anti-rupturing strength. In this regard, preferably the main tube body layer is formed of at least one member selected from a group consisting of urethane resin, nylon and polyethylene, and the reinforcing layer is formed of metal netting in the form of knit fabric of metallic filaments.
Further, according to the present invention, there is also provided a method for manufacturing a flexible tube having a laminated multi-layer structure including an outer layer including a main tube body layer formed of a thermoplastic synthetic resin in a predetermined thickness, and a reinforcing layer provided integrally on the inner side of the main tube body layer, and an inner layer formed of a thin film of air tight and low friction material provided on the inner side of the reinforcing layer, the method comprising the steps of: forming the inner layer by wrapping an elongated strip of a thin film sheet around a core rod in such a way that opposite lateral sides of the thin film sheet are overlapped one on the other to a predetermined degree to provide a thick wall portion of a predetermined width extending longitudinally of and at one angular position of the inner layer; etching outer peripheral surfaces of the inner layer on the core rod; forming a reinforcing mesh layer on and around the inner layer by knitting metal filaments directly on and around etched outer surfaces of the inner layer; and forming the main tube body layer by laminating a thermoplastic resin on and around the reinforcing mesh layer.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawing which show by way of example its preferred embodiments. Needless to say, the present invention should not be construed as being limited to particular embodiments shown.